This invention relates generally to mining operations and, more particularly, to grinding mills utilized in mining operations.
Currently, there are two main types of mills employed in mining operations, geared mills and gearless mills. Geared mills typically are power limited to approximately 9000 horsepower per pinion or 18,000 horsepower for a dual-pinion driven mill. Gearless mills, also called Ring Motor mills are employed when a mine operator desires a mill of greater than 18,000 horsepower, or in such cases, where the economics benefits justify the use of a Gearless mill with less than 18,000 horsepower. A typical gearless mill""s ring motor works similar to a synchronous machine with a direct current field exciter. Accordingly, a gearless grinding mill motor includes a stator including a bore and one or more field windings. A rotor assembly extends at least partially through the stator bore and includes a rotor core and a rotor shaft/structure extending through the rotor core. The rotor core includes one or more armature windings. The stator of a gearless grinding mill is large and cannot fit in a Vacuum Pressure Impregnation (VPI) tank, which is typically utilized during the manufacture of stators for synchronous machines and other rotating and linear electrical machines. Available VPI tanks typically have a diameter of twelve feet or less and a depth of ten feet or less. Additionally, a grinding mill""S stator is sufficiently large that the stator can not be transported in one piece.
Accordingly, the stator is split into several segments that are individually transported from a motor manufacturer""s plant to a customer""s site. The number of segments depends on a size of the stator and shipping conditions or restrictions but typically the stator is segmented into three or four or more segments. After the segments arrive at the final assembly site, the segments are reassembled. Because segmenting the stator involves segmenting the core including the windings or coils, reassembling the stator involves reconnecting or closing the windings at the customer""s site. However, closing the windings at a customer""s site involves significant costs associated with employing skilled laborers (winders) to close the windings and a higher risk of contamination because the customer""s site (a mine) is typically dirty and constitutes a contaminated environment. Additionally, the closed winding can not be factory tested as a winding assembled in a factory can be.
Accordingly, a need exists for providing a large gearless grinding mill including stator windings that are closed at a factory and not segmented for transfer to a customer""s site.
In one aspect, a method for fabricating a gearless grinding mill motor is provided. The method includes fabricating a plurality of linear stator portions and assembling a grinding mill stator from the linear stator portions.
In another aspect, the method includes fabricating a plurality of substantially identical linear stator portions each including a substantially identical linear drive wherein one drive is programmed to be a master drive. Each stator portion includes a plurality of dimensions each less than three meters, and each linear stator portion further includes one three phase winding electrically connected to the linear drive. Each three phase winding is substantially galvanically isolated from all other three phase windings. The method further includes assembling the linear stator portions to form a stator including a bore therethrough.
In another aspect, a grinding mill is provided. The grinding mill includes a stator including a bore therethrough and a plurality of linear stator portions. The grinding mill further includes a shell rotatably mounted at least partially within the bore and at least one winding mounted on the shell and separated from the stator by an air gap.